1. Field of the Invention
The present invention relates to a solar power charging system, and more particularly to a solar power charging system for charging a power generated from a solar battery into an electric double layer capacitor at a high efficiency.
2. Description of the Related Art
Advanced power systems integrate the solar power charging system which includes the solar battery and the electric double layer capacitor, so that a power is generated during the daytime and the generated power is consumed in the night in order to respond to environmental and energy requirements. This solar system is, for example, disclosed in Japanese laid-open patent publication No. 10-66281. It is important for the solar power charging system to increase the efficiency of supplying the generated power to the capacitor.
FIG. 1A is a block diagram illustrative of a power system including a conventional solar power charging system. FIG. 1B is a block diagram illustrative of the conventional solar power charging system shown in FIG. 1A. This conventional power system is also disclosed in Japanese laid-open patent publication No. 9-292851. A conventional solar power charging system 70 includes a solar battery 71, a rectifier 72 such as a diode, a first DC-DC converter 73, and an electric double layer capacitor 74. The conventional solar power charging system 70 is connected to a second DC-DC converter 75. The second DC-DC converter 75 is connected to an indicator 76. The solar power charging system 70 stores a power. The second DC-DC converter 75 receives the power from the solar power charging system 70 and converts the voltage of the power. The power with the converted voltage is supplied to the indicator 76 for indicating the converted voltage level of the power.
With reference to FIG. 1B, the power voltage is supplied from the solar battery 71 through the rectifier 72 to the first DC-DC converter 73. The power voltage generated by the solar battery 71 varies depending on sunshine conditions. The first DC-DC converter 73 converts the variable power voltage into a predetermined constant voltage level. The power with the predetermined constant voltage level is then supplied from the first DC-DC converter 73 to the electric double layer capacitor 74, so that the electric double layer capacitor 74 is charged at the predetermined constant voltage level.
Charging the capacitor at the constant voltage level means that about a half of the generated power from the solar battery can theoretically be charged to the capacitor. This means that as long as the capacitor is charged at the constant voltage level, the efficiency of charging the capacitor is low.
The solar battery has a maximum power condition based on a variable generated power voltage level. The maximum power condition depends on a relationship between voltage and current from the solar battery. The method of charging the capacitor at the predetermined constant voltage level is incapable of satisfying the maximum power condition.
In the above circumstances, the development of a novel solar power charging system free from the above problems is desirable.
Accordingly, it is an object of the present invention to provide a novel solar power charging system free from the above problems.
It is a further object of the present invention to provide a novel solar power charging system capable of charging a capacitor under the maximum power condition.
The present invention provides a solar power charging system comprising: a voltage converter for converting a voltage level of an original voltage generated by a solar battery into generate a charging voltage and for charging a capacitor by the charging voltage; and a duty ratio control circuit electrically coupled to the voltage converter for supplying a driving clock to the voltage converter for allowing the voltage converter to operate based on the driving clock, wherein the duty ratio control circuit adjusts a duty ratio of the driving clock based on a maximum charge power which depends on the original voltage generated by the solar battery.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.